With the ultimate aim of comparing capillariopathy in the cerebral cortex of diabetes with that in the retina, an initial study was made of trypsin digest preparations of samples of normal cerebral cortex. The cerebral capillaries had wider lumina and less regularly spaced mural cells but were nevertheless similar to those of the retina. In a single patient who died with severe diabetic retinopathy the cortical capillaries showed no abnormality.